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Applied Optics

Applied Optics


  • Vol. 14, Iss. 7 — Jul. 1, 1975
  • pp: 1652–1663

Combined reflection and transmission thin-film ellipsometry: a unified linear analysis

R. M. A. Azzam, M. Elshazly-Zaghloul, and N. M. Bashara  »View Author Affiliations

Applied Optics, Vol. 14, Issue 7, pp. 1652-1663 (1975)

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A scheme of combined reflection and transmission ellipsometry on light-transmitting ambient–film–substrate systems is proposed and the required sample design and instrument operation are investigated. A comparative study of the sensitivity of external and internal reflection and transmission ellipsometry is carried out based on unified linear approximations of the exact equations. These approximations are general in that an arbitrary initial film thickness is assumed. They are simple, because a complex sensitivity function is introduced whose real and imaginary projections determine the psi (ψ) and delta (Δ) sensitivity factors. Among the conclusions of this paper are the following. (1) External reflection ellipsometry near the Brewster angle of a transparent ambient–substrate system is extremely sensitive to the presence of very thin interfacial films. For example, films as thin as 10−5 Å of gold are readily detectable on glass substrates at an angle of incidence 0.3° below the Brewster angle, assuming a measuring wavelength of 5461 Å with an ellipsometer of 0.05° precision. (2) The formation of thin nonabsorbing films at the interface between transparent ambient and substrate media is not detectable, to first order, as a change in the ellipsometric angle ψ by either internal or external reflection or transmission ellipsometry. (3) The film-detection sensitivity of transmission ellipsometry increases monotonically with angle of incidence. (4) For each angle of external incidence there is a corresponding angle of internal incidence that leads to the same values of the reflection and transmission sensitivity functions. These angles are interrelated by Snell's law. (5) The ranges of validity of the linear approximation in reflection and transmission ellipsometry are comparable. The case of total internal reflection ellipsometry may lead to strong nonlinear behavior of ψ and Δ as functions of the film thickness in the range below 0.05 of the wavelength of light.

© 1975 Optical Society of America

Original Manuscript: August 20, 1974
Published: July 1, 1975

R. M. A. Azzam, M. Elshazly-Zaghloul, and N. M. Bashara, "Combined reflection and transmission thin-film ellipsometry: a unified linear analysis," Appl. Opt. 14, 1652-1663 (1975)

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  1. E. Passaglia, R. R. Stromberg, J. Kruger, Eds., Ellipsometry in the Measurement of Surfaces and Thin Films, Natl. Bur. Std. Misc. Pub. 256 (U.S. Govt. Printing Office, Washington, 1964);N. M. Bashara, A. B. Buckman, A. C. Hall, Eds., Proceedings of the Symposium on Recent Developments in Ellipsometry (North-Holland, Amsterdam, 1969) [Surface Sci. 16, 1969].
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  4. It may be necessary to choose a measuring wavelength such that these requirements are met over the thickness range of interest.
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  10. D. E. Confer, R. M. A. Azzam, N. M. Bashara, to be published.
  11. In differential reflection spectroscopy, we measure the fractional change of reflectance δRν/Rν, where Rν = RνRν*. We can write δRν/Rν = (δRν/Rν) + (δRν*/Rν*) = 2Re(δRν/Rν) = [2Re(Qν)] (δd1/d1), where Qν is given by Eq. (14). This result is in agreement with one obtained by McIntyre and Aspnes (Ref. 3).
  12. The zero-thickness psi and delta sensitivity factors for reflection ellipsometry were introduced by R. C. Smith and M. Hacskaylo (the first of Refs. 1, p. 83), who used the restricted Drude linear approximation.
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  21. Burge and Bennett, Ref. 16, have pointed out several errors in the linear approximations used by earlier workers.
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  23. Internal reflection ellipsometry was used by E. C. Chan, J. P. Marton, J. Appl. Phy. 43, 4027 (1972), to study metal deposits on glass slides.See also M. J. Dignam, B. Rao, M. Moskovits, R. B. Stobie, Can. J. Chem. 49, 1115 (1971). [CrossRef]
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  26. R. M. A. Azzam, N. M. Bashara, J. Opt. Soc. Am. 61, 1236 (1971). [CrossRef]

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